34
Calibration
3.4
Barometer
The barometer is factory calibrated and should rarely need to be recalibrated. The barometer is used for DO
calibration, %Local measurements, and for virtual vented depth measurements. Verify that the barometer is accurately
reading “true” barometric pressure and recalibrate as necessary.
Laboratory barometer readings are usually “true” (uncorrected) values of air pressure and can be used “as is” for
barometer calibration. Weather service readings are usually not “true”,
i.e.
they are corrected to sea level and cannot
be used until they are “uncorrected”. Use this approximate formula:
True BP in mmHg=[Corrected BP in mmHg] - [2.5* (Local altitude in ft. above sea level/100)]
Example:
Corrected BP = 759 mmHg
Local altitude above sea level = 978 ft
True BP = 759 mmHg - [2.5*(978ft/100)] = 734.55 mmHg
Barometer Calibration
1.
Push the
Cal
key, then select
Barometer
.
2.
Select
Calibration value
then enter the correct “true” barometric
pressure.
NOTE:
The measurement units during calibration are dictated by
what is enabled in the sensor setup menu. Be sure to enter
in the correct units.
• BP in mmHg=25.4 x BP inHg
• BP in mmHg=0.750062 x BP mb
• BP in mmHg=51.7149 x BP psi
• BP in mmHg=7.50062 x BP kPa
• BP in mmHg=760 x BP atm
3.
Select
Accept Calibration
(
Figure 50
). “Calibration successful!” will
be displayed in the message area.
Figure 50
Calibrate Barometer
8.
Rinse the sensor in clean water then dry.
NOTE:
If the data is not stabilized after 40 seconds, gently rotate
the sensor or remove/reinstall the calibration cup to make
sure that no air bubbles are in the conductivity cell.
If you get calibration error messages, check for proper
sensor immersion, verify the calibration solutions is fresh,
the correct value has been entered into the handheld, and/
or try cleaning the sensor.
Conductivity Calibration
(continued)
